Organic Photosensitive Device with an Electron-Blocking and Hole-Transport Layer

ABSTRACT

The present disclosure provides a photosensitive device. The photosensitive device includes a donor-intermix-acceptor (PIN) structure. The PIN structure includes an organic hole transport layer; an organic electron transport layer; and an intermix layer sandwiched between the hole transport organic material layer and the electron transport organic material layer. The intermix layer includes a mixture of an n-type organic material and a p-type organic material.

This is a continuation application of U.S. patent application Ser. No.14/012,692, filed Aug. 28, 2013, now U.S. Pat. No. ______, the entiredisclosure of which is incorporated herein by reference.

BACKGROUND

Image sensors are integrated circuit devices that include a plurality ofsensor elements or pixels formed in a semiconductor substrate. Thesensor elements are used for sensing a volume of exposed light projectedtowards the semiconductor substrate. For image sensors, a desire existsto advance quantum efficiency (QE) when pixel size is shrunk down. QErefers to the response with which the image sensor converts light toelectrons within each pixel. Various techniques are used to form imagesensors and to improve QE and sensitivity. For example, organicmaterials are used to form image sensors. However, in the existing imagesensors with organic materials, existed are various issues that includehigh dark current and low power conversion efficiency.

Therefore, what is needed is a structure of an organic image sensor anda method making the same to address the above issues.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isemphasized that, in accordance with the standard practice in theindustry, various features are not drawn to scale. In fact, thedimensions of the various features may be arbitrarily increased orreduced for clarity of discussion.

FIG. 1 illustrates a sectional view of a photosensitive deviceconstructed according to aspects of the present disclosure.

FIG. 2 illustrates a sectional view of a photosensitive deviceconstructed according to aspects of the present disclosure in one ormore embodiments.

FIG. 3 illustrates a diagrammatical view of a photosensitive deviceconstructed according to aspects of the present disclosure in one ormore embodiments.

FIGS. 4, 5 and 6 are diagrammatical views of various chemicals of thephotosensitive device in FIG. 3.

FIG. 7 illustrates a diagrammatical view of dark currents of variousphotosensitive devices constructed according to aspects of the presentdisclosure in various examples.

FIG. 8 illustrates a diagrammatical view of photo current of the variousphotosensitive devices constructed according to aspects of the presentdisclosure in various examples.

FIG. 9 is a table of diagrammatical view of characteristic data of thevarious photosensitive devices constructed according to aspects of thepresent disclosure in various examples.

FIG. 10 illustrates a sectional view of a photosensitive structureconstructed according to aspects of the present disclosure in oneembodiment.

FIG. 11 illustrates a perspective view of a photosensitive structureconstructed according to aspects of the present disclosure in anotherembodiment.

DETAILED DESCRIPTION

It is to be understood that the following disclosure provides manydifferent embodiments, or examples, that may benefit from the presentinvention. Specific examples of components and arrangements aredescribed below to simplify the present disclosure. These are, ofcourse, merely examples and are not intended to be limiting. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.Moreover, the formation of a first feature over or on a second featurein the description that follows may include embodiments in which thefirst and second features are formed in direct contact, and may alsoinclude embodiments in which additional features may be formedinterposing the first and second features, such that the first andsecond features may not be in direct contact.

An organic photosensitive device and the method making the same aredescribed below according to aspects of the present disclosure invarious embodiments. The organic photosensitive device includes animaging sensor (such as a photodiode) designed to sense light or anenergy conversion device (such as solar cell) to receive light forelectrical energy conversion.

Referring to FIG. 1, illustrated is a sectional view of a photosensitivedevice 10. In one embodiment, the photosensitive device 10 includes animaging sensor, such as a photodiode. In another embodiment, thephotosensitive device 10 includes a solar cell designed for electricalenergy conversion from light. The photosensitive device 10 includesvarious organic materials configured to achieve its function and addressvarious issues to enhance performance and quality. Therefore, thephotosensitive device 10 is also referred to as organic photosensitivedevice. The photosensitive device 10 is formed on a substrate, such as aglass substrate, a semiconductor substrate or other suitable substrate.Various organic material layers may be disposed by a suitable technique,such as spin coating, knife-over-edge coating, spray coating, slot-diecoating, rotogravure printing, screen printing or other suitabletechnique. Other materials (such as electrode materials) may be disposedby physical vapor deposition (PVD), plating or other suitable technique.

The photosensitive device 10 has a donor-intermix-acceptor (PIN)structure. Especially, the photosensitive device 10 includes a holetransport (p-type) layer 14 and an electron transport (n-type) layer 16.The photosensitive device 10 further includes an intermix layer 12interposed between the hole transport layer 14 and the electrontransport layer 16. The PIN structure is designed for photo sensing withfurther electron blocking and leakage reduction, thereby improvingphotocurrent and optical characteristics of the photosensitive device10.

In one embodiment, the hole transport layer 14 includes an organic holetransport material and therefore is also referred to as an organic holetransport layer 14. In another embodiment, the electron transport layer16 includes an organic electron transport material and therefore isreferred to as an organic electron transport layer 16.

The intermix layer 12 functions as a photoactive layer of thephotosensitive device 10. The intermix layer 12 includes an organicmaterial, therefore is also referred to as organic photoactive layer. Inthe present embodiment, the intermix layer 12 includes a mixture(blending) of an organic hole transport (organic p-type) material and anorganic electron transport (organic n-type) material. In anotherembodiment, the intermix layer 12 includes a mixture (blending) of ann-type fullerene derivative and a p-type conjugate polymer. In aparticular embodiment, the intermix layer 12 includes a mixture of theorganic hole transport material of the hole transport layer 14 and theorganic electron transport material of the electron transport layer 16.The intermix layer 12 may have a uniform composition or alternativelyhas a gradient composition that varies from the hole transport layer 14to the electron transport layer 16.

The hole transport layer 14 may include one or more hole transportmaterials and may include one or more films with respective holetransport materials. In one embodiment, the hole transport layer 14includes a conjugate polymer to function for hole transport and furtherfor electron blocking. In one example, the hole transport layer 14includes Poly(3-hexylthiophene-2,5-diyl) (or P3HT). In another example,the hole transport layer 14 includesPoly(2-methoxy-5-(3′-7′-dimethyloctyloxy)-1,4-phenylenevinylene (orMDMO-PPV).

In another embodiment, the hole transport layer 14 includes two films: afirst p-type material film and a second p-type material film of aconjugated polymer (such as P3HT or MDMO-PPV) disposed on the firstp-type material film. In one example, the first p-type material filmincludes poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (orPEDOT:PSS). In an alternative example, the first p-type material filmincludes one of molybdenum oxide (MoO₃), nickel oxide (NiO), copperoxide (CuO), vanadium oxide (V₂O₅), tungsten oxide (WO₃) and acombination thereof.

The electron transport layer 16 may include one or more electrontransport materials and may include one or more films with respectiveelectron transport materials. In one embodiment, the electron transportlayer 16 includes an n-type fullerene derivative to function forelectron transport and hole blocking. In one example, the electrontransport layer 16 includes Phenyl-C61-Butyric-Acid-Methyl Ester (orPCBM). In another example, the electron transport layer 16 may includephenyl-C70-butyric acid methyl ester (PC70BM), phenyl C71 butyric acidmethyl-ester (PC71BM) or a combination thereof.

In another embodiment, the electron transport layer 16 includes twofilms: a first n-type material film of a fullerene derivative (such asPCBM) and a second n-type material film disposed on the first n-typematerial film. In one example, the second n-type material film includeslithium fluorine (LiF). Alternatively, the second n-type material filmincludes a material selected from the group consisting of LiF, calcium(Ca), magnesium (Mg), calcium oxide (CaO), magnesium oxide (MgO),aluminum oxide(Al₂O₃), or organic electron transport material layer suchas bathocuproine (BCP),1,3,4-Oxadiazole,2,2-(1,3-phenylene)bis[5-[4-(1,1-dimethylethyl)phenyl]](or OXD-7). The formation of the electrodes may use a suitabletechnique, such as PVD.

Back to the intermix layer 12, the intermix layer 12 includes a mixtureof the hole transport material of the hole transport layer 14 and theelectron transport material of the electron transport layer 16 accordingto one embodiment. In one example, the intermix layer 12 includes amixture of P3HT and PCBM (simply referred to as P3HT:PCBM).

In another embodiment, the intermix layer 12 includes a p-type materialof a conjugated polymer and an n-type material of a fullerenederivative. For one example, the p-type material of a conjugated polymerincludesPoly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl] thieno[3,4-b]thiophenediyl]] (orPTB7). For another example, an n-type material of a fullerene derivativeincludes PC70BM or PC71BM. In one example, the intermix layer 12includes a mixture (blend) of PTB7 and PC70BM, simply referred to asPTB7:PC70BM. In other embodiments, the intermix layer 12 includesvarious mixture of one or more p-type materials and one or more n-typematerials.

The formation of the electron blocking layer 12 includes spin coating,spray coating, inkjet printing, thermal evaporated process or othersuitable method.

The photosensitive device 10 further includes two electrodes configuredon the two ends of the PIN structure. Particularly, the photosensitivedevice 10 includes an anode 18 adjacent the hole transport layer 14 anda cathode 20 adjacent the electron transport layer 16, as illustrated inFIG. 1. In one embodiment, the anode 18 includes a transparentconductive material, such as indium tin oxide (tin-doped indium oxide,or ITO). Alternatively, transparent conductive material may includealuminum-doped zinc oxide (AZO) or indium gallium zinc oxide (IGZO). Thedeposition of the transparent electrode may include PVD, pulsed laserdeposition or other suitable deposition technique.

In another embodiment, the cathode 20 includes aluminum (Al).Alternatively, the cathode 20 includes a conductive material selectedfrom the group consisting of Al, titanium (Ti), silver (Ag) or acombination thereof. The formation of various electrodes may use asuitable technique, such as PVD. The electrodes may be configureddifferently. For example, if the photosensitive device 10 is configuredsuch that the light is directed to the photoactive layer from anothersides (n-type layer), then the transparent conductive material may beused to form the cathode 20.

Different advantages may present in various embodiments of thephotosensitive device 10. In one embodiment, the photosensitive device10 includes P3HT inserted between the photoactive layer (such asP3HT:PCBM or PTB7:PC70BM) and a hole transport layer (such asPEDOT:PSS). P3HT functions as an electron blocking layer to reduce theleakage current. P3HT is essentially an outstanding donor material thatcan absorb light with 400-600 nm in wavelength and creates an extradonor/acceptor interface close to the bottom of the composite layers toenhance short circuit current density. P3HT as an inserted electronblocking layer substantially increases blocking electron capability toreduce dark current density. Alternatively, MDMO-PPV may be insertedbetween the photoactive layer (such as P3HT:PCBM or PTB7:PC70BM) and ahole transport layer (such as PEDOT:PSS), functioning as an electronblocking layer to reduce the leakage current. In furtherance of theembodiment, the electron transport layer may be eliminated from thephotosensitive device 10.

FIG. 2 illustrates a sectional view a photosensitive device 30constructed according to aspects of the present disclosure. Thephotosensitive device 30 may be one embodiment of the photosensitivedevice 10. In one embodiment, the photosensitive device 30 includesvarious organic materials configured to achieve its function withenhanced performance and quality. The photosensitive device 30 includesan electron blocking layer inserted between the hole transport layer andthe photoactive layer.

The photosensitive device 30 is formed on a substrate, such as asemiconductor substrate or other suitable substrate (such as a glasssubstrate). Various organic material layers of the photosensitive device30 may be formed by a suitable technique, such as spin coating,knife-over-edge coating, spray coating, slot-die coating, rotogravureprinting, thermal evaporated process or screen printing.

The photosensitive device 30 includes an electrode 32. The electrode 32includes a conductive material, such as titanium (Ti), titanium nitride(TiN), gold (Au), or silver (Ag). The deposition of the electrode 32 mayinclude PVD, plating or other suitable deposition technique.

The photosensitive device 30 includes a hole transport and electronblocking layer 34 disposed on the electrode 32. In various embodiments,the hole transport and electron blocking layer 34 includes PEDOT:PSS, oralternatively includes one of molybdenum oxide (MoO₃), nickel oxide(NiO), copper oxide (CuO), vanadium oxide (V₂O₅), tungsten oxide (WO₃)and a combination thereof.

The photosensitive device 30 includes an organic hole transport andelectron blocking layer 36 disposed on the hole transport and electronblocking layer 34. In one embodiment, the organic hole transport andelectron blocking layer 36 includes P3HT, MDMO-PPV or other organicelectron blocking material.

The photosensitive device 30 includes an organic photoactive layer 38disposed on the organic hole transport and electron blocking layer 36.The organic photoactive layer 38 may include a conjugated polymer, afullerene derivative, or a combination thereof. In the presentembodiment, the organic photoactive layer 38 includes one or moreconjugated polymer and one or more fullerene derivative in mixture. Theorganic photoactive layer 38 may have a uniform composition or a gradedcomposition with the concentrations of the conjugated polymer and thefullerene derivative varying from the bottom surface to the top surface.In one example, the organic photoactive layer 38 includes P3HT:PCBM. Inanother example, the organic photoactive layer 38 includes PTB7:PC70BM.In yet another embodiment, the organic photoactive layer 38 includes amixture of one or more fullerene derivative (PCBM, PC71BM, or PC71BM)and one more conjugated polymer (P3HT, or PTB7).

In one embodiment of the organic photoactive layer 38 that includesPTB7:PC71BM blending and the organic hole transport and electronblocking layer includes H3HT, the photoactive layer has a high externalquantum efficiency (EQE) (>60%) and an adjustable opticalcharacteristics due to the maximum absorption range. Particularly, theabsorption ranges of PC71BM, P3HT, and PTB7 are at 450 nm, 550 nm and650 nm, respectively.

The photosensitive device 30 includes an organic electron transport andhole blocking layer 40 disposed on the organic photoactive layer 38. Inone embodiment, the organic electron transport and hole blocking layer40 includes fullerene derivative, n-type conjugated polymer orcombination thereof. The organic electron transport and hole blockinglayer 40 may include one or more material, such as a combination of afullerene derivative and an n-type conjugated polymer. The organicelectron transport and hole blocking layer 40 may include one or morefilms each with respective electron transport material. In one example,the organic electron transport and hole blocking layer 40 includes PCBM.

The photosensitive device 30 includes an electron transport and holeblocking layer 42 disposed on the organic electron transport and holeblocking layer 40. The electron transport and hole blocking layer 42includes lithium fluorine (LiF), titanium oxide (TiO₂), zinc oxide(ZnO), tantalum oxide (Ta₂O₅), zirconium oxide (ZrO₂) or a combinationthereof. The formation of the electron transport and hole blocking layer34 may include PVD, chemical vapor deposition (CVD) or other suitabledeposition technique.

The photosensitive device 30 includes a transparent electrode 44disposed on the electron transport and hole blocking layer 42. Thetransparent electrode 44 includes a conductive material that istransparent to the light to be sensed by the photosensitive device 30during the applications. In one example, the transparent electrode 44includes ITO. In other example, the transparent electrode 44 includesaluminum-doped zinc oxide (AZO) or indium gallium zinc oxide (IGZO). Thedeposition of the transparent electrode may include PVD, pulsed laserdeposition or other suitable deposition technique.

FIG. 3 illustrates a photosensitive device 45 with various materials ofrespective energy band structures in diagrammatical view. Various energylevels are labeled in FIG. 3 in unit eV. The photosensitive device 45may be one example of the photosensitive device 30. The photosensitivedevice 45 includes an electron blocking layer inserted between the holetransport layer and the photoactive layer. Particularly, thephotosensitive device 45 includes an electrode of an ITO layer, a holetransport layer of PEDOT:PSS, a p-type blocking layer, an organicphotoactive layer of P3HT:PCBM, a n-type blocking layer, a LiF and anelectrode of an Al layer sequentially configured as illustrated in FIG.3. Alternatively, the organic photoactive layer may include PTB7:PC70BM.

The p-type electron blocking layer includes a conjugated polymer. In oneembodiment, the p-type electron blocking layer includes P3HT asillustrated in FIG. 4. P3HT is inserted between the hole transport layerof PEDOT:PSS and the organic photoactive layer. P3HT can absorb lightwith 400-600 nm in wavelength and creates an extra donor/acceptorinterface to enhance short circuit current density. P3HT as an insertedelectron blocking layer substantially increases blocking electroncapability to reduce dark current density.

In another embodiment, the p-type electron blocking layer includesMDMO-PPV as illustrated in FIG. 5. MDMO-PPV functions as an electronblocking layer to reduce the leakage current. In a particular example,MDMO-PPV is inserted between the hole transport layer of PEDOT:PSS andthe photo active layer of P3HT:PCBM.

The p-type electron blocking layer of a conjugated polymer provides aproper structure to effectively block electron and reduce the leakage.The energy bandgap (or bandgap) of the electron blocking layer isdefined as bandgap =|HOMO−LUMO|, where HOMO is the highest occupiedmolecular orbital of the conjugated polymer and LUMO is the lowestunoccupied molecular orbital of the conjugated polymer. In the presentembodiment, HOMO ranges between 5 eV and 5.4 eV, LUMO ranges between 2.8eV and 3.2 eV, and the bandgap ranges between 2 eV and 2.4 eV. In thefirst example where P3HT is used as the p-type electron blocking layer,HOMO=5 eV, LUMO=3 eV and bandgap=2 eV. In the second example whereMDMO-PVV is used as the p-type electron blocking layer, HOMO=5.4 eV,LUMO=3.0 eV and bandgap=2.4 eV.

The n-type electron blocking layer includes a fullerene derivative. Inone embodiment, the n-type electron blocking layer includes PCBM asillustrated in FIG. 6. The n-type electron blocking layer of a fullerenederivative provides a proper structure to effectively block electron andreduce the leakage. The energy bandgap (or bandgap) of the n-typeelectron blocking layer is defined as bandgap =|HOMO−LUMO|, where HOMOis the highest occupied molecular orbital of the fullerene derivativeand LUMO is the lowest unoccupied molecular orbital of the fullerenederivative. In the present embodiment, HOMO ranges between 6.1 eV and6.7 eV, LUMO ranges between 3.2 eV and 4.5 eV, while the bandgap rangesbetween 1.6 eV and 3.0 eV. In the present embodiment where PCBM is usedas the n-type electron blocking layer, HOMO=6.1 eV, LUMO=3.7 eV andbandgap=2.4 eV.

Due to respective energy levels of the various materials, the electronsfrom ITO are blocked from entering to the organic photoactive layer bythe p-type electron blocking layer of the conjugated polymer, and theholes from Al are blocked from entering the organic photoactive layer bythe n-type electron blocking layer of the fullerene derivative,effectively reducing the current leakage.

FIGS. 7-9 are characteristic data of various photosensitive devicesincluding a photosensitive device 45. FIG. 7 illustrates the darkcurrents 46 of the various photosensitive devices in a diagrammaticalview. FIG. 8 illustrates the photo currents 48 of the variousphotosensitive devices in a diagrammatical view. FIG. 9 is a table 50that lists parameters and configurations of the various photosensitivedevices.

Particularly, the various photosensitive devices associated with FIGS.7-9 include a first photosensitive device, a second photosensitivedevice, and a third photosensitive device that is one example of thephotosensitive device 45. Compare to the third photosensitive device,the first photosensitive device does not include the hole blocking layerof LiF. The second photosensitive device includes LiF as a hole blockinglayer (with a thickness of 0.8 nm in this example).

In FIG. 7, the horizontal axis is the voltage “V” (in volts or V)applied to the photosensitive device, and the vertical axis is thecurrent density “J” (in A/cm²) through the photosensitive device. Thedata are collected from the first, second and third photosensitivedevices, respectively. Particularly, the photosensitive device 45 in thepresent example includes the electron blocking layer of P3HT and furtherincludes a hole blocking layer of LiF. It is illustrated that the darkcurrent of the photosensitive device 45 is reduced compared to otherphotosensitive devices.

In FIG. 8, the horizontal axis is the voltage “V” (in volts or V)applied to the photosensitive device, and the vertical axis is thecurrent density “J” (in mA/cm²) through the photosensitive device. Thedata are collected from the first, second and third photosensitivedevices, respectively. It is illustrated that the amplitude of the photocurrent of the photosensitive device 45 is increased compared to otherphotosensitive devices.

In the table 50 of FIG. 9, the first, second and third photosensitivedevices are noted as “w/o LiF”, “with LiF” and ‘with LiF and P3HTlayer”, respectively. The various parameters include the open-circuitvoltage “V_(oc)” in V, the short circuit current “J_(sc)” in mA/cm2, thefill factor “FF” in % and the power conversion efficiency “PCE” in %.The data in the table 50 further illustrate the improved performance ofthe photosensitive device 45 compared to other photosensitive devices.

FIG. 10 is a sectional view of a photosensitive structure 52 having aplurality of photosensitive devices (such as photosensitive devices 10,30 or 45) integrated in an array. In the present example forillustration, the photosensitive structure 52 includes three exemplaryunit pixels 54 (54A, 54B and 54C). Each unit pixel includes aphotosensitive device.

The photosensitive structure 52 includes a substrate 56. The substrate56 includes silicon, such as crystalline silicon. The substrate 56 mayalternatively or additionally include other semiconductor material suchas germanium, gallium arsenic, or indium phosphide. The substrate 56 mayinclude various p-type doped regions and/or n-type doped regionsconfigured and coupled to form various devices and functional features.All doping features may be achieved using a process such as ionimplantation or diffusion in various steps and techniques.

The photosensitive structure 52 may further includes various isolationfeatures 58 formed in the substrate 56. In one example, the isolationfeatures 58 include shallow trench isolation (STI) features formed inthe substrate 54, defining various active regions. In the presentembodiment, the STI features define active regions for respective unitpixels (such as 54A, 54B and 54C) and each unit pixel includes aphotosensitive device.

The photosensitive structure 52 includes various devices, such as fieldeffect transistors (FETs) formed in the substrate 56 and configured toform read-out circuits 60.

The photosensitive structure 52 also includes an interconnect structure62 configured to couple various devices (including the photosensitivedevices and read-out circuits) to form a functional circuit. Theinterconnect structure 62 includes an inter-layer dielectric (ILD) layerdisposed on the substrate 56, a plurality of inter-metal dielectric(IMD) layers, and various interconnect features formed in the ILD layerand the IMD layers. The interconnect features are conductive featuresand are distributed in various metal layers. The interconnect featuresinclude contact features, via features and metal lines. Particularly,the contact features are configured between metal one and thesemiconductor substrate, coupling the metal one and semiconductorsubstrate. The via features are configured between adjacent metallayers, coupling adjacent metal layers. The metal lines providehorizontal routings in respective metal layers. In one embodiment, theinterconnect features include copper and are formed using damascenetechnology. The interconnect features may include other conductivematerials, such as copper alloy, titanium, titanium nitride, tantalum,tantalum nitride, tungsten, polysilicon, metal silicide, or combinationsthereof. In one embodiment, silicide may be formed on the gate and/orsource/drain for reduced contact resistance. In another embodiment,aluminum is used for interconnect with aluminum technology known in theart. For example, the aluminum alloy including copper and silicon may beused to form interconnect features. In this case, a metal etchingprocess may be used to form metal lines. In another embodiment, tungstenmay be used to form tungsten plugs for various contact features and viafeatures with better filling effect.

The photosensitive structure 52 includes a plurality of photosensitivedevices 64 disposed on the interconnect structure 62, such as variousphotosensitive devices 62 formed within respective active regions 54.The photosensitive devices 64 include pixel electrodes 32, aphotoelectrical conversion layer 66 and a transparent electrode 44.

Each photosensitive device 64 includes a pixel electrode 32 patternedand configured to be coupled with respective read-out circuit 60. In oneexample, the pixel electrode 32 includes a conductive material, such astitanium (Ti), titanium nitride (TiN), gold (Au), silver (Ag) oraluminum (Al). The deposition of the electrode 32 may include PVD,plating or other suitable deposition technique.

The transparent electrode 44 is disposed on the photoelectricalconversion layer 66. The transparent electrode 44 includes a conductivematerial that is transparent to the light to be sensed by thephotosensitive device 30 during the applications. In one example, thetransparent electrode 44 includes ITO. In other example, the transparentelectrode 44 includes aluminum-doped zinc oxide (AZO) or indium galliumzinc oxide (IGZO). The deposition of the transparent electrode mayinclude PVD, pulsed laser deposition or other suitable depositiontechnique.

The photoelectrical conversion layer 66 includes various material layers(of the photosensitive device) sandwiched between the transparentelectrode 44 and the pixel electrode 32. For example, thephotoelectrical conversion layer 66 includes various layers 34, 36, 38,40 and 42 of the photosensitive device 30.

FIG. 11 illustrates a perspective view of a photosensitive device 70constructed according to aspects of the present disclosure in otherembodiments. The photosensitive device 70 may be one example of thephotosensitive device 30. The photosensitive device 70 includes anelectron blocking layer inserted between the hole transport layer andthe organic photoactive layer.

Particularly, the photosensitive device 70 includes a substrate 72, suchas a glass substrate or other suitable substrate. The photosensitivedevice 70 is formed on the substrate 72. The electrodes may be formed byPVD or other suitable technique. Various organic material layers may beformed by a suitable technique, such as spin coating, knife-over-edgecoating, spray coating, slot-die coating, rotogravure printing, thermalevaporated process or screen printing.

The photosensitive device 70 includes a transparent electrode 44disposed on the substrate 72. The transparent electrode 44 includes aconductive material that is transparent to the light to be sensed by thephotosensitive device 70 during the applications. In one embodiment, thetransparent electrode 44 includes ITO. In other embodiment, thetransparent electrode 44 includes AZO or IGZO. The deposition of thetransparent electrode may include PVD, pulsed laser deposition or othersuitable deposition technique.

The photosensitive device 70 includes a hole transport and electronblocking layer 34 disposed on the transparent electrode 44. In oneembodiment, the hole transport and electron blocking layer 34 includesPEDOT:PSS. In an example, the thickness of the PEDOT:PSS ranges betweenabout 30 nm and about 40 nm. In an alternative embodiment, the holetransport and electron blocking layer 34 includes one MoO₃, NiO, CuO,V₂O₅ and a combination thereof.

The photosensitive device 70 includes an organic hole transport andelectron blocking layer 36 disposed on the hole transport and electronblocking layer 34. In one embodiment, the organic hole transport andelectron blocking layer 36 includes P3HT. In one example, P3HT may beformed various suitable conditions that include mixing with additive,coating and annealing. The annealing is implemented in an annealingtemperature ranging from about 130° C. and about 170° C. for a durationranging from about 10 minutes to about 30 minutes.

The photosensitive device 70 includes an organic photoactive layer 38disposed on the organic hole transport and electron blocking layer 36.In the present embodiment, the organic photoactive layer 38 includes amixture of a conjugated polymer and a fullerene derivative. In oneexample, the organic photoactive layer 38 includes a blending of P3HTand PCBM. In furtherance of the example, the thickness ranges betweenabout 120 nm and about 150 nm. The ratio of P3HT and PCBM is about 1:0.8in molecular weight. In another example, the organic photoactive layer38 includes a blending of PTB7:PC70BM. In furtherance of the example,the ratio of PTB7 and PC70BM is about 1:1.5 in molecular weight.

In other example, the organic photoactive layer 38 includes a blend ofPTB7:PC71BM. In another embodiment, the organic photoactive layer 38includes a combination of PCBM, PC71BM, PC70BM, P3HT, PTB7, or a subsetthereof.

The photosensitive device 70 includes an electron transport and holeblocking layer 42 disposed on the organic photoactive layer 38. Theelectron transport and hole blocking layer 42 includes LiF, titaniumoxide (TiO₂), zinc oxide (ZnO), tantalum oxide (Ta₂O₅), zirconium oxide(ZrO₂) or a combination thereof. The formation of the electron transportand hole blocking layer 34 may include PVD, chemical vapor deposition(CVD) or other suitable deposition technique. In one particular example,the electron transport and hole blocking layer 42 of LiF has a thicknessranging between about 0.8 nm and about 1 nm. The electron transport andhole blocking layer 42 of LiF may be formed by PVD with a depositionrate of about 0.2 A/s.

The photosensitive device 70 includes an electrode 32 disposed on theelectron transport and hole blocking layer 42. The electrode 32 includesa conductive material, such as titanium (Ti), titanium nitride (TiN),gold (Au), silver (Ag) or aluminum (Al). The deposition of the electrode32 may include PVD, plating or other suitable deposition technique. Inone particular example, the electrode 32 of Al has a thickness of about100 nm and is formed by PVD with a deposition rate of about 3 A/s.

Different advantages may present in various embodiments. In oneembodiment, P3HT is inserted between the hole transport layer and thephotoactive layer. In one example, P3HT has a high-molecular weight witha weight-average molecular weight (Mw) of 30000˜60000 g/mol and apolydispersity index less than about 1.5.

In other examples, various parameters are improved by inserting a P3HTlayer, as described below. The dark current density of thephotosensitive device is reduced to less than 10% of a photosensitivedevice without the inserting layer P3HT. The short-circuit currentdensity is increased by 10˜20% relative to that of a photosensitivedevice without the P3HT layer. The power conversion efficiency isincreased by 10˜20% relative to that of a photosensitive device withoutthe P3HT layer.

Particularly, P3HT absorbs light with 400-600 nm in wavelength andcreates an extra donor/acceptor interface to enhance short circuitcurrent density. P3HT layer substantially increases the blockingelectron capability to reduce dark current density.

Thus, the present disclosure provides a photosensitive structure. Thephotosensitive structure includes a donor-intermix-acceptor (PIN)structure. The PIN structure further includes an organic hole transportlayer; an organic electron transport layer; and an intermix layersandwiched between the hole transport organic material layer and theelectron transport organic material layer. The intermix layer includes amixture of an n-type organic material and a p-type organic material.

In one embodiment of the photosensitive structure, the intermix layerincludes a mixture of an n-type fullerene derivative and a p-typeconjugated polymer. In another embodiment, the organic hole transportlayer includes an organic p-type material; the organic electrontransport layer includes an organic n-type material; and the intermixlayer includes a mixture of the organic n-type material and the organicp-type material.

In another embodiment, the organic electron transport layer includesPhenyl-C61-Butyric-Acid-Methyl Ester (PCBM). In another embodiment, theorganic hole transport layer includes Poly(3-hexylthiophene-2,5-diyl)(P3HT) orPoly(2-methoxy-5-(3′-7′-dimethyloctyloxy)-1,4-phenylenevinylene(MDMO-PVV).

In another embodiment, the intermix layer includes a mixture of P3HT andPCBM (P3HT:PCBM) or a mixture ofPoly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl] thieno[3,4-b]thiophenediyl]] (PTB7)and phenyl-C70-butyric acid methyl ester (PC70BM).

In yet another embodiment, the organic hole transport layer includesP3HT; the organic electron transport layer includes PCBM; and theintermix layer includes a mixture of P3HT and PCBM.

The photosensitive structure may further include a hole transport layerconfigured such that the organic hole transport layer is disposedbetween the hole transport layer and the intermix layer. In oneembodiment, wherein the hole transport layer includespoly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS). Inanother embodiment, the hole transport layer includes one of molybdenumoxide (MoO₃), nickel oxide (NiO), copper oxide (CuO), vanadium oxide(V₂O₅) and a combination thereof.

The photosensitive structure may further include an electron transportlayer configured such that the organic electron transport layer isdisposed between the electron transport layer and the intermix layer. Inone embodiment, the electron transport layer includes one of lithiumfluorine (LiF), titanium oxide (TiO₂), zinc oxide (ZnO), tantalum oxide(Ta₂O₅), zirconium oxide (ZrO₂) or a combination thereof.

The present disclosure also provides a photosensitive structure inanother embodiment. The photosensitive structure includes a holetransport layer; an organic photoactive layer; and an organic electronblocking layer sandwiched between the hole transport layer and theorganic photoactive layer. The organic photoactive layer includes amixture of a fullerene derivative and a conjugated polymer.

In one embodiment, the organic photoactive layer includes a mixture ofPoly(3-hexylthiophene-2,5-diyl) (P3HT) andPhenyl-C61-Butyric-Acid-Methyl Ester (PCBM).

In another embodiment, the organic photoactive layer includes a mixtureofPoly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl] thieno[3,4-b]thiophenediyl]] (PTB7)and phenyl-C70-butyric acid methyl ester (PC70BM).

In yet another embodiment, the organic electron blocking layer includesan organic material selected from the group consisting ofPoly(3-hexylthiophene-2,5-diyl) (P3HT), andPoly(2-methoxy-5-(3′-7′-dimethyloctyloxy)-1,4-phenylenevinylene(MDMO-PVV).

In yet another embodiment, the hole transport layer includespoly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS).

In yet another embodiment, the photosensitive structure further includesan n-type fullerene derivative configured such that the organicphotoactive layer is disposed between the n-type fullerene derivativeand the organic electron blocking layer, wherein the n-type fullerenederivative includes PCBM.

In yet another embodiment, the photosensitive structure further includesan electron transport layer configured such that the n-type fullerenederivative is disposed between the electron transport layer and theorganic photoactive layer, wherein the electron transport layer includesone of lithium fluorine (LiF), titanium oxide (TiO₂), zinc oxide (ZnO),tantalum oxide (Ta₂O₅), zirconium oxide (ZrO₂) or a combination thereof.

The present disclosure also provides another embodiment of aphotosensitive structure. The photosensitive structure includes a holetransport layer; an organic hole transport layer disposed on the holetransport layer; an organic photoactive layer disposed on the organichole transport layer; an organic electron transport layer disposed onthe organic photoactive layer; and an electron transport layer disposedon the organic electron transport layer.

In one embodiment, the hole transport layer includespoly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS); theorganic hole transport layer includes one ofPoly(3-hexylthiophene-2,5-diyl) (P3HT) andPoly(2-methoxy-5-(3′-7′-dimethyloctyloxy)-1,4-phenylenevinylene(MDMO-PVV); the organic electron transport layer includesPhenyl-C61-Butyric-Acid-Methyl Ester (PCBM); the organic photoactivelayer includes P3HT:PCBM; and the electron transport layer includes oneof lithium fluorine (LiF), titanium oxide (TiO₂), zinc oxide (ZnO),tantalum oxide (Ta₂O₅), zirconium oxide (ZrO₂) or a combination thereof.

The foregoing has outlined features of several embodiments so that thoseskilled in the art may better understand the detailed description thatfollows. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method comprising: forming apoly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) holetransport layer over a first electrode; forming an organicpoly(3-hexylthiophene-2,5-diyl) (P3HT) hole transport layer over thePEDOT:PSS hole transport layer; forming an organic photoactive layerover the organic P3HT hole transport layer, wherein the organicphotoactive layer includes a mixture of poly (PTB7) andphenyl-C70-butyric acid methyl ester (PC70BM) or a mixture of P3HT andphenyl-C61-butyric-acid-methyl ester (PCBM); forming an electrontransport layer over the organic photoactive layer, wherein the organicphotoactive layer has a gradient composition that varies from theorganic P3HT hole transport layer to the electron transport layer; andforming a second electrode over the electron transport layer.
 2. Themethod of claim 1, wherein the forming the electron transport layerincludes: forming a first electron transport layer on the organicphotoactive layer, wherein the first electron transport layer includesPCBM; and forming a second electron transport layer over the firstelectron transport layer.
 3. The method of claim 1, wherein the electrontransport layer includes lithium, fluorine, titanium, zinc, tantalum,zirconium, oxygen, or a combination thereof.
 4. The method of claim 1,wherein the forming the electron transport layer includes performing adeposition process with a deposition rate of about 0.2 A/s.
 5. Themethod of claim 1, wherein the forming the organic photoactive layerincludes performing a spin coating process, a knife-over-edge coatingprocess, a spray coating process, a slot-die coating process, arotogravure printing process, or a screen printing process.
 6. Themethod of claim 1, wherein the forming the first electrode and thesecond electrode includes performing a physical vapor depositionprocess.
 7. The method of claim 1, wherein the forming the electrontransport layer includes performing a physical vapor deposition processor a chemical vapor deposition process.
 8. A method comprising: forminga hole transport layer on a first electrode; forming an organicpoly(3-hexylthiophene-2,5-diyl) (P3HT) hole transport layer on the holetransport layer; forming an organic photoactive layer having texturedsurfaces on the organic P3HT hole transport layer, wherein the organicphotoactive layer includes a mixture of poly (PTB7) andphenyl-C70-butyric acid methyl ester (PC70BM) or a mixture of P3HT andphenyl-C61-butyric-acid-methyl ester (PCBM); forming an electrontransport layer on the organic photoactive layer; and forming a secondelectrode over the electron transport layer.
 9. The method of claim 8,wherein the forming the hole transport layer includes forming an organicmaterial layer that includes poly(3,4-ethylenedioxythiophene)poly(styrenesulfonate) (PEDOT:PSS).
 10. The method of claim 8, whereinthe forming the hole transport layer includes forming an organicmaterial layer that includespoly(2-methoxy-5-(3′-7′-dimethyloctyloxy)-1,4-phenylenevinylene(MDMO-PVV).
 11. The method of claim 8, wherein the forming the electrontransport layer includes forming an organic material layer that includesPCBM.
 12. The method of claim 11, wherein the organic material layer isa first electron transport layer, the method further comprising forminga second electron transport layer over the first electron transportlayer, such that the second electron transport layer is disposed betweenthe first electron transport layer and the second electrode.
 13. Themethod of claim 12, wherein the second electron transport layer includeslithium and fluorine.
 14. The method of claim 8, wherein the secondelectrode includes a transparent conductive material.
 15. A methodcomprising: forming a hole transport layer over a first electrode;forming an organic poly(3-hexylthiophene-2,5-diyl) (P3HT) hole transportlayer over the hole transport layer; forming an organic photoactivelayer over the organic P3HT hole transport layer, wherein the organicphotoactive layer includes a mixture of P3HT andphenyl-C61-butyric-acid-methyl ester (PCBM), and further wherein a ratioof a molecular weight of the P3HT to the PCBM is about 1:0.8; forming anelectron transport layer over the organic photoactive layer; and forminga second electrode over the electron transport layer.
 16. The method ofclaim 15, wherein the forming the hole transport layer includes formingan organic material layer that includes poly(3,4-ethylenedioxythiophene)poly(styrenesulfonate) (PEDOT:PSS) orpoly(2-methoxy-5-(3′-7′-dimethyloctyloxy)-1,4-phenylenevinylene(MDMO-PVV).
 17. The method of claim 15, wherein the forming the organicP3HT hole transport layer includes performing an annealing process. 18.The method of claim 17, wherein the annealing process implements anannealing temperature of about 130° C. and about 170° C. for about 10minutes to about 30 minutes.
 19. The method of claim 15, wherein theforming the electron transport layer includes performing a firstdeposition process and the forming the second electrode includesperforming a second deposition process, wherein a deposition rate of thefirst deposition process is less than a deposition rate of the seconddeposition process.
 20. The method of claim 19, wherein the firstdeposition process and the second deposition process are physical vapordeposition processes.